A human vertebrae has a rearwardly projecting portion known as a spinous process. Bending of the spine, particularly extension of the spine, can cause the spinous processes of adjacent vertebrae to move toward each other. This constricts the space in the spinal canal and foramina and may cause pain. Such pain may be exacerbated when the spinal canal or nerve roots exiting the canal are constricted by natural degeneration of the spine, such as by spinal stenosis or degenerative disc disease. Such pain may be treated by positioning an implant in a space between adjacent spinous processes to maintain a predetermined distance between the adjacent spinous processes, thereby providing a minimum amount of space between the spinous processes.
Generally there are two types of spinal stenosis: (1) hard or rigid spinal stenosis or (2) soft or dynamic spinal stenosis. In both cases, spinal stenosis may be caused by excessive growth of tissue due to degeneration, loss of disc height, excessive load in a particular area of the spine as well disorders such as spondilolisthesis where the normal relative position and/or orientation of the adjacent vertebrae have been modified.
A difference between the two types of spinal stenosis is that, generally, dynamic spinal stenosis may be treated with distraction of the vertebra at the affected level while hard stenosis generally requires removal of the tissue that obstructs the spinal canal or foramina at the affected level. In the case of tissue removal, the surgical treatment typically results in some loss of stability to the spine. Therefore, it is preferable to increase the stability of the spinal segment by inserting an interspinous process spacer (“ISS”) between the spinous processes of the adjacent vertebrae to increase the stiffness of the segment and/or to restrict motion of that segment.
Some current implants are made of separate pieces that require insertion from both sides of the spinous processes using a posterior approach that necessitates rather wide openings into a patient, cutting both left and right thoracolumbar fascia, as well as stripping the multifidus muscles from their attachments. It is desirable to provide an implant for insertion between the spinous processes of adjacent vertebrae which are inserted through a single opening in a minimal invasive approach and may be held firmly in position between the vertebrae. It is desirable for the surgical incision and surgical pathway to extend laterally into the space between the adjacent spinous processes, thereby preserving major ligaments and musculature of the spine at the impacted level.